chore(deps): update dependency @edx/frontend-platform to v1.15.6

Author: renovate-bot

package-lock.json

@@ -35,7 +35,7 @@
   "devDependencies": {
     "@edx/brand": "npm:@edx/[email protected]",
     "@edx/frontend-build": "9.2.2",
-    "@edx/frontend-platform": "^1.15.1",
+    "@edx/frontend-platform": "1.15.6",
     "@edx/paragon": "19.22.1",
     "codecov": "3.8.3",
     "enzyme": "3.11.0",